Hydrogen is used as a raw material for producing ammonia, methanol, and the like and also used as an essential material of hydrogenation for producing a saturated compound. Further, if used as a main material of fuel cells as one of clean alternative energy, hydrogen can be an alternative to current fossil fuel and thus has been highly anticipated as a future energy source.
Conventionally, hydrogen has been produced by a method of reforming fossil fuel such as naphtha and natural gas, a method of bringing iron into contact with steam at a high temperature, a method of making a reaction between alkali metal and water, a method of electrolyzing water, and the like.
However, these methods basically require a lot of energy and thus cannot be said as economical methods. In particular, the method of reforming fossil fuel has a problem of generating a large amount of carbon dioxide, and the method of electrolyzing water has a problem of short-life electrodes and a problem in processing oxygen generated. Due to the above-described problems, it actually costs much to complete the facilities for producing hydrogen.
Thus, in recent years, a method of directly converting water or organic materials into hydrogen with solar energy by photolysis has been studied as one of methods for producing hydrogen an alternative to fossil fuel. This method is a key technology capable of securing the most desirable eco-friendly energy system.